Quick Summary: Frost covers for outdoor plants act as a protective blanket against sudden cold snaps and light frosts, safeguarding your beloved greenery. These simple yet effective barriers trap warmth, prevent ice crystal formation on leaves, and allow your plants to survive chilly nights, ensuring a healthier garden.
Hello fellow garden lovers! Pearl Roach here from EcoPatchy, ready to chat about something that can make even the most seasoned gardener a little anxious: unexpected frost. You’ve nurtured your plants, watched them grow, and then… BAM! A cold snap threatens all your hard work. But don’t worry, keeping your plants safe from frost doesn’t have to be complicated or expensive. We’re going to dive into the wonderful world of frost covers – your garden’s cozy blanket for those chilly nights.
I know how frustrating it can be. You wake up, peek outside, and see those tell-tale signs of frost on your precious herbs or delicate flowers. It feels like a gardening emergency! That’s why understanding frost covers is such a vital skill for any gardener, especially when you’re just starting out. They’re like a superhero cape for your plants, ready to deploy when the temperature drops.
This guide is designed to be your friendly sidekick in the fight against frost. We’ll break down exactly what frost covers are, why they’re so important, and all the different types you can use. I’ll walk you through how to choose the right one and, of course, how to use them effectively. Get ready to give your plants the best possible chance to thrive, even when the weather tries to surprise us!
What Are Frost Covers and Why Do Plants Need Them?
Simply put, frost covers (also known as frost cloths, row covers, or horticultural fleece) are designed to protect your plants from freezing temperatures. They’re a physical barrier that acts like a greenhouse, trapping heat that radiates from the soil and the plant itself overnight. This creates a microclimate around your plant that is several degrees warmer than the surrounding air.
Why is this so crucial? Well, many plants, especially tender annuals, seedlings, and even some perennials, have delicate tissues that can be damaged or killed by frost. When water inside plant cells freezes, it expands, forming ice crystals. These crystals can rupture the cell walls, leading to wilting, browning, and ultimately, the death of the affected parts of the plant. Think of it like this: if your plant’s internal fluids freeze, it’s like a mini explosion happening inside its leaves and stems!
Understanding Frost vs. Freezing
It’s helpful to know a little about what’s happening. Frost forms when the surface temperature of plants drops to or below the freezing point of water (0°C or 32°F) and the surrounding air is also cool and humid. Even if the air temperature is just above freezing, radiant cooling from the plant’s surface can cause frost to form. This is especially common on clear, still nights.
Freezing temperatures are damaging for a different, though related, reason. Even without visible frost, sustained temperatures below a plant’s tolerance can cause cells to die. Frost covers help with both scenarios by trapping heat and preventing direct contact with freezing air.
The Damage Frost Can Cause
- Cellular Damage: Ice crystals rupture plant cells, leading to tissue death.
- Wilting and Discoloration: Affected leaves often turn brown, black, or translucent.
- Reduced Yield: Flowers and developing fruits can be damaged, impacting harvest.
- Plant Death: Severe or prolonged frost can kill young or sensitive plants entirely.
The good news is that with a little preparation and the right frost cover, you can significantly reduce or eliminate this damage. It’s about proactive care for your garden buddies!
Types of Frost Covers for Outdoor Plants
When we talk about frost covers, there’s a whole spectrum of options, from simple DIY solutions to ready-made products. The best choice for you will depend on your budget, the size of your plants, and how often you anticipate needing protection.
Fabric Frost Covers (Horticultural Fleece)
These are probably the most common and versatile type of frost cover. They are made from lightweight, breathable synthetic fabrics (often polypropylene) that allow air, water, and sunlight to pass through while also trapping heat.
- Weight and Thickness: They come in different weights, typically measured in grams per square meter (gsm).
- Lightweight (15-30 gsm): Good for protecting against light frost (up to -3°C / 27°F) and extending the growing season in spring and fall. They allow maximum light penetration.
- Mediumweight (30-50 gsm): Offers more warmth, protecting against moderate frosts (down to -6°C / 21°F).
- Heavyweight (50+ gsm): Provides the most protection, suitable for more severe frosts (down to -8°C / 18°F and colder), but they block more light.
- How to Use: These can be draped directly over plants, secured around the base with rocks or soil. For larger areas or taller plants, they are often supported by hoops, frames, or stakes to keep the fabric from touching the foliage directly, which helps prevent freezing. You can purchase them as large sheets or in pre-cut sizes. Many garden supply stores also sell “tree wrap” or “frost protection bags” made from similar material for individual shrubs or young trees.
- Where to Buy: Your local garden center, online retailers like Amazon, or specialized horticultural suppliers. You may also find it by the yard at fabric stores, but ensure it’s the breathable, gardening-specific type.
Plastic Sheeting and Tarps
While not ideal for direct, long-term contact with plants, plastic sheeting (like painter’s drop cloths, greenhouse plastic, or even heavy-duty garbage bags) can be used carefully. It offers good protection against wind and frost but lacks breathability.
- Pros: Excellent at blocking wind and rain; readily available and often inexpensive.
- Cons: Crucially, plastic must NOT touch the plant leaves or stems. It traps moisture, which can lead to condensation and fungal diseases. It also doesn’t allow air circulation, which can cause plants to overheat during the day or suffocate. Sunlight can also be filtered too much depending on the type.
- How to Use: Always create a frame or support structure (like hoops or a simple A-frame) to hold the plastic several inches away from the plants. Ensure good ventilation by leaving one side open or creating an adjustable opening during the day. It’s best for short-term, emergency protection.
For more on using plastic covers safely in gardening, the Gardening Know How website offers practical advice on avoiding common pitfalls.
DIY Solutions and Household Items
Don’t have a fancy frost cloth? No problem! Many common household items can be repurposed in a pinch:
- Old Blankets or Sheets: Natural fibers like cotton or wool can offer some insulation. Like plastic, they should ideally be supported and not directly touching plants. They need to be removed in the morning so they don’t stay wet and heavy.
- Buckets or Plastic Tubs: For individual plants, simply placing an overturned bucket or tub over them before nightfall can provide significant protection. Ensure it’s large enough not to crush the plant.
- Cardboard Boxes: Similar to buckets, these can offer a quick shield, but they disintegrate if they get wet.
- Newspaper: Loosely crumpled newspaper can add a layer of insulation. Again, direct contact is less ideal for moisture reasons, but it can be tucked around plants or used as a temporary measure.
Cloches and Cold Frames
These are more permanent or semi-permanent structures designed to protect plants, often used for seedlings or extending the growing season.
- Cloches: These are essentially individual plant covers, often dome-shaped. Traditionally made of glass (like old bell jars), nowadays they are commonly made of plastic. They trap heat and protect from frost while allowing light and air in. They are excellent for protecting individual vegetables or small shrubs.
- Cold Frames: These are low, box-like structures with a transparent lid (usually glass or plastic). They are placed over garden beds and can provide a very stable, protected environment for overwintering plants or starting seedlings early. They offer more robust protection than a simple cloth but require more space and investment. The Penn State Extension has detailed guides on building and using cold frames.
Choosing the Right Frost Cover for Your Plants
With all these options, how do you pick the best one? Consider these factors:
1. Plant Type and Size
Small Seedlings / Tender Annuals: Lightweight fleece, cloches, or even overturned pots can work well.
Vegetable Gardens (Rows): Roll-out fleece laid over hoops (creating a tunnel effect) is very efficient.
Mature Shrubs / Small Trees: Heavier fleece wraps or specifically designed tree protectors are best.
Container Plants: Can be grouped together and covered with a larger sheet of fleece or brought into a more sheltered spot. If they are large and immovable, use tree wraps or draped fleece.
Sensitive Herbs (e.g., Basil, Rosemary): These often require the most protection. Lightweight fleece draped over a frame, or bringing pots indoors on threatened nights, is a good strategy.
2. Expected Temperature Drop
A light frost (just below freezing) might only require a lightweight fleece. A hard frost (significantly below freezing) will need a heavier fabric, multiple layers, or a more substantial structure like a cold frame.
| Frost Cover Type | Protection Level (Approx.) | Best For | Breathability |
|---|---|---|---|
| Lightweight Fleece (15-30 gsm) | Up to -3°C (27°F) | Seedlings, tender annuals, extending season | High |
| Mediumweight Fleece (30-50 gsm) | Up to -6°C (21°F) | Vegetables, small shrubs | High |
| Heavyweight Fleece (50+ gsm) | Up to -8°C (18°F) or lower | Hardy plants, extended protection | Moderate to High |
| Plastic Sheeting / Tarps | High (if not touching plant) | Emergency protection, wind barrier | Very Low (requires ventilation) |
| Cloches / Cold Frames | Variable; generally good | Seed starting, overwintering, sensitive plants | Moderate (depends on design) |
3. Longevity and Reusability
Fabric frost covers are generally reusable for several seasons if cared for properly. Plastic can be reused but may degrade in sunlight faster. Cloches and cold frames are investments that can last for many years.
4. Budget
DIY methods using household items are the cheapest. Lightweight frost cloths are relatively inexpensive, while heavy-duty fleece, cloches, and cold frames represent a larger initial investment.
How to Use Frost Covers Effectively: Step-by-Step
Putting your frost cover to work is straightforward. Here’s a general guide, with variations depending on the type of cover you’re using.
Step 1: Check the Weather Forecast
This is your cue! Pay attention to overnight low temperatures. If the forecast predicts frost or temperatures below what your specific plants can tolerate (especially for tender seedlings or newly planted items), it’s time to act.
Step 2: Gather Your Supplies
Have your chosen frost cover(s) ready. This might also include stakes, hoops, bricks, rocks, or clips to secure the cover.
Step 3: Prepare the Plants (Optional, but Helpful)
If you’re using fabric covers, ensure plants are well-watered. Moist soil holds heat better than dry soil and can radiate warmth up to the plants overnight. You can also mulch around the base of plants; this acts as insulation for the roots and stems.
Step 4: Apply the Frost Cover
This is the crucial part. The goal is to create a microclimate warmer than the ambient air.
For Fabric Frost Cloths:
- Drape Gently: Carefully unfurl the fabric over your plants.
- Avoid Direct Contact (Ideally): If possible, use hoops, stakes, or branches to keep the fabric from resting directly on leaves or flowers. Frost can form on the fabric and then freeze the plant parts it touches. For many light frosts, this isn’t a critical issue, but for colder temperatures, it makes a big difference.
- Secure Firmly: Use rocks, bricks, soil, or garden staples to anchor the edges of the fabric to the ground. This prevents it from blowing away and seals in warmth. Ensure there are no large gaps.
- For Tunnels: If covering rows of vegetables, use hoops (bent PVC pipe, metal rods, or even sturdy branches) to create an arched tunnel. Drape the fabric over the hoops and secure the edges.
For Plastic Sheeting, Tarps, and DIY Covers:
- Always Use a Frame: Plastic MUST be supported so it does not touch the plants. Build a frame, use hoops, or even tall stakes to create a tent-like structure.
- Seal Edges: Secure the edges of the plastic to the ground
